Benchmarking against Zed's rope crate

[mainrs]

The zed editor has a custom rope implementation: https://github.com/zed-industries/zed/tree/main/crates/rope

Would be cool to see a comparison of the performance! I don't think it has a builder API, but the rest seems to be available.

[noib3]

I had some cross-rope benchmarks at https://github.com/noib3/rope-benches/. They're written over a Rope abstraction, so it shouldn't be too hard to add a new impl. I'd merge a PR to that repo if you want to add it.